Postage metering systems are well known in the art. A postage metering system applies evidence of postage, commonly referred to as postal indicium, to an envelope or other mailpiece (directly or on a label to be applied thereto) and accounts for the value of the postage dispensed.
Presently, there are two basic postage metering system types: closed systems and open systems. In a closed system, the system functionality is solely dedicated to postage metering activity. Examples of closed metering systems include conventional digital and analog (mechanical and electronic) postage meters wherein a dedicated printer is securely coupled to a metering or accounting function. In a closed system, since the printer is securely coupled and dedicated to the meter, printing evidence of postage cannot take place without accounting for the evidence of postage. In an open system, the printer is not dedicated to the metering activity, freeing system functionality for multiple and diverse uses in addition to the metering activity. Examples of open metering systems include personal computer (PC) based devices with single/multi-tasking operating systems, multi-user applications and digital printers. Open system indicia printed by the non-dedicated printer are made secure by including addressee information in the encrypted evidence of postage printed on the mailpiece for subsequent verification.
Conventional analog closed system postage meters (both mechanical and electronic) have heretofore physically secured the link between printing and accounting. The integrity of the physical meter box has been monitored by periodic inspections of the meters. Digital closed system postage meters typically include a dedicated digital printer coupled to a device that provides metering (accounting) functionality. Digital printing postage meters have removed the need for the physical inspection that was required with analog systems by cryptographically securing the link between the accounting and printing mechanisms.
In such digital closed systems, the dedicated printer and the metering (accounting) device may be located in the same device and/or at the same location when placed in operation. Alternatively, the dedicated printer may be located in a first location (i.e., the local location where indicia are to be printed), and the metering (accounting) device may be located in a remote location, such as a provider's data center. In the latter situation, it is still necessary for the dedicated printer to be a secure device having cryptographic capabilities so that postage printing information, such as an indicium, received from the metering (accounting) device, and the metering (accounting) device itself, can be authenticated.
One particular implementation of a closed system includes a secure postage printing device that stores and prints indicia for specific postage denominations that were previously dispensed by an approved postal security device (PSD) associated with a data center. In operation, a user sends a request to purchase postage to the data center in the form of a request for a particular number of indicia for one or more particular postage denominations (e.g., twenty $0.37 indicia and twenty $0.74 indicia). In response, the data center generates an appropriate number of postage data records (one for each requested indicium) and transmits them to the postage printing device where they are stored until printed, refunded or erased at a refurbishment facility. In addition, for data integrity and/or security reasons, the postage requests are digitally signed and the postage downloads are encrypted and digitally signed using symmetric cryptography and secret encryption keys that are associated with the particular postage printing device (i.e., a particular user account) and known to the postage printing device and the data center. This type of postage printing device may also be freely and independently (i.e., without the participation of or the need to get authorization from the postage provider) transferred to a new user, in which case the new user is able to use any postage data records that are stored at the time of the transfer. However, as will be appreciated, if the encryption keys are left unchanged after the transfer, the old user may be susceptible to and/or blamed for fraudulent acts committed by the new user. Thus, there is a need for a method for securing a postage printing device and an inventory of postage data records held thereby when the device is transferred among users.